The effectiveness of green roofs in reducing building energy consumptions across different climates. A summary of literature results

Green roofs are an interesting technology that has attracted worldwide attention because of the multidisciplinary benefits, involving the improvement of stormwater management, the mitigation of the urban heat island effect, the prolonged lifespan of the roof membrane, the enhancement of urban aesthetic, the creation of recreational spaces, and the possibility to generate energy savings for building heating and cooling. Several papers dealt with green roofs, spacing from quantification of runoff quality and quantity, to the evaluation of plant and substrate intrinsic characteristics, to the social aspects related to the installation of vegetated surfaces in densely populated cities. A big share of research has investigated the thermal performances of different green roof solutions in the attempt to assess the effect on the building energy demand. A lot of studies have been conducted through experimental research on properly instrumented green roofs or by numerical simulations implemented in different environments or even by developing and validating thermo-physical models that describe the interaction between the green roof and the surrounding environment. Although the relevant number of papers dealing with the thermal performance of vegetated roofs in the literature, quantitative estimations of the reduction of building energy consumption due to green roofs are not easily found. The paper presents a comprehensive literature review to summarize the relevant findings in terms of energy savings produced by a green roof to offer a suitable answer to the question of the energy effectiveness of such a solution and quantitatively report the results obtained across different climates.